Hmm, I've never seen that happen before? My only guess is that since you're in FL, and I'm guessing that you're not painting in an environmentally controlled area, that the humidity is causing the problem.

If , IF it we me i would 400 wet sand the whole rear bumper , have it ready to paint and go get it painted . ^Like he said its not gonna look really good rattle canned . I mean Theres just no spread/spray to a rattle can the metallic would streak tremendously . The paint would run probably 40 a pint , and probably a quart of clear would be 60 or less , and then 2-3hrs labor , you'd be looking at probably 250 tops to get a get professional job . Atleast thats what i would charge.

I would take it to a body shop and get it professionally done. A spray can does not atomize the paint aswell as a spray gun. It shouldn't be to expensive $200-300 dollars at most. For future notice, don't do any exterioir painting with a can.

You are never going to get a good finish with a rattle can. Why did you feel you needed to try and reclear the bumper?

You can get a good finish with rattle can, it's a little trickier than professional clear, but it can be done. However, you should NEVER paint urethane parts with rattle can clear. It will crack over time. Body shops use an additive to make the clear have some flex to it so that it doesn't crack when the bumper flexes. I would drop the can and take it to a shop instead.